a) Field of the Invention
The present invention relates to a friction clutch, especially for a motor vehicle.
The invention is concerned more particularly with a clutch of the pull to release type, one embodiment of which is described and shown in the documents FR-A-2 304 826, FR-A-2 653 195 (U.S. Pat. No. 5,113,989), DE-A-2 815 971.
b) Description of Related Art
A clutch of this type comprises a friction disc which is disengageably coupled in rotation to a rotatable drive shaft (the crankshaft of the engine in the case of a motor vehicle), a control member which is arranged to control disengagement of the friction clutch from the drive shaft when an axial tractive force is exerted on it, and a clutch release bearing which is arranged to work axially in traction on the control member of the clutch.
Such a clutch, as shown in the document FR-A-2 304 826, may be of the mechanically controlled type, that is to say of the type which has a fork for control of the declutching operation, which is made in the form of a lever pivoted on the clutch casing, with its inner end working axially on a sliding sleeve, one end of which is coupled axially, for example, to the outer ring of the ball bearing which is part of the clutch release bearing.
As described in that document, the use of the mechanical declutching control fork, in a direction opposite to that which provides the declutching function, enables an element coupled to the inner ring of the ball bearing of the clutch release bearing to be coupled, in fixed relationship in an axial tractive mode, with a component which works on a diaphragm or on declutching levers, this coupling being obtained by means of resilient mating which may also be called clipping.
Various clutch designs are also known which include a hydraulic actuating device that includes at least one actuating piston, one end of which works on the clutch release bearing so as to urge the said release bearing axially in a first direction, in order to disengage the clutch when the hydraulic actuating device is supplied with fluid from a pressurized fluid source, such as for example a clutch cylinder.
One example of such a hydraulically actuated clutch is described and shown in the document U.S. Pat. No. 3,955,660, in which the actuating piston is made in the form of a cylindrical sleeve mounted for sliding movement on a cylindrical guide surface fixed to the clutch casing.
Such a hydraulically actuated clutch, which no longer includes a mechanical actuating fork for the clutch release bearing, does not enable initial fastening, by means of resilient mating, to be obtained between the output member of the clutch release bearing and the member which acts on the pressure plate.
Such a type of clutch also has other disadvantages, among which are those related to the supply of pressurized fluid to the actuating chamber of the hydraulic piston, which makes it necessary to provide at least one pressurized fluid supply duct which extends inside the clutch casing, and which can be connected hydraulically to the actuating chamber and to the pressurized fluid source, and in connection with which, in the interest of its good mechanical strength, it is in general necessary to provide means for preventing rotation of the actuating piston.
Such means are described in the document DE-A-2 815 971. In this latter, the hydraulic actuating device further includes a mechanical lever having a body, a first end portion coupled in axial translation to the piston and pivoted on the latter about a pivot axis at right angles to the axis of axial sliding movement of the piston, and a second end portion, with the said lever passing through a cylindrical hole in the wall of the casing.
In practice it is the second end portion of the lever that extends through the wall of the casing, being flush with the latter.
With this type of embodiment, it is not possible to carry out initial fastening, by resilient mating, between the output member of the clutch release bearing and the member which acts on the pressure plate.